I've decided to write this entry before I could actually master these tools because I don't think I will afterwards (I'd be too old to type). So here it goes:

ReSharper - yes! I will probably need a ReSharper blog tag. This thing is good for everything! Its XAML smart intellisense is a gem, as well as the various options you get when writing WPF code or XAML

Snoop - this is a very small tool that acts like a WPF FireBug. It can select an element, show properties, even change some of them

Pistachio - this is a Visual Studio project resource browser. Give it the project and you can see the brushes, the style, the templates, the usages

Expression Blend - the de facto Microsoft tool for editing XAML and working with design stuff. Not only it is not free, but it is also buggy. Unfortunately, I have a hunch I will have to use it in the near future to work with WPF styles

ShowMeTheTemplate - Small application that explores the WPF default templates for various controls